Sunday, January 4, 2015

New Cancer Study Raises Many Questions, Flies in Face of Facts

According to a new study by Johns Hopkins University, published this past week in the journal Science, if you get cancer (like my prostate cancer) it is  mostly just "bad luck".  The abstract of the paper in question, by Cristian Tomasetti and Bert Vogelstein,  reads:

"Some tissue types give rise to human cancers millions of times more often than other tissue types. Although this has been recognized for more than a century, it has never been explained. Here, we show that the lifetime risk of cancers of many different types is strongly correlated (0.81) with the total number of divisions of the normal self-renewing cells maintaining that tissue’s homeostasis. These results suggest that only a third of the variation in cancer risk among tissues is attributable to environmental factors or inherited predispositions. The majority is due to “bad luck,” that is, random mutations arising during DNA replication in normal, noncancerous stem cells. This is important not only for understanding the disease but also for designing strategies to limit the mortality it causes."

Which on its face is nothing sort of amazing, and basically - taken at face value- the implication is people can do whatever the hell they want: smoke, eat nitrite -laden sausages daily, work in a place full of carcinogens, live near a toxic waste dump and even ingest Roundup-ready corn regularly and they needn't fret. If they happen to get cancer it's because of the "luck of the draw" since it's a 67% probability it's "bad luck" in having cells that don't divide normally - or die at the right time.

As one Denver Post article notes:

"The research might bolster arguments that cancer can't be prevented."

Which then means that the work of assorted organizations such as 'Breast Cancer Awareness', and the Prostate Cancer Foundation are just based on empty promises and hollow recommendations that don't matter in the end. As the article goes on to note this would then imply  summoning fewer resources for prevention (forget that colonoscopy or PSA test if this is true!) and instead direct the energy toward "diagnosing the disease in its early stages"

Basically, Tomasetti and Vogelstein found that tissue types that have more stem-cell divisions are more prone to mutations that can lead to cancers.  Thus, they indicate that only one-third of the variation in cancer risk might be due to environmental factors or inherited predispositions.

How is this assessed statistically? Basically, using a quantifier called the coefficient of determination.  This is expressed V = 100 r^2 %, where r is the Pearson product-moment coefficient. For example, in their study the authors found r = 0.81 (i.e. lifetime risk of cancers with the total number of divisions of self-renewing cells maintaining tissue homeostasis).

Then one finds:  V = 100 (0.81)^2 =   0.656 (100 %) = 65.6%

Or nearly 66 percent, rounded off. Hence, two thirds of the variation accounted for by "bad luck" in the author's parlance, or cells not dividing normally.

Yet, this large variation outside of environmental risk, for example, can't explain the numerous "cancer clusters" around the country, areas affected by toxic chemical intrusions and which yield higher than expected numbers of cancer cases. See e.g.

As a final point, the authors clearly grasp that "correlation isn't causation" so that no matter how high their correlation coefficient (leading to how much variation can be explained by 'random factors') the specter of cancer risk factors remains and can't be so easily dismissed - and I'd warrant not artificially limited to 1/3 or less of the explained variation. Indeed, having done similar regression studies with solar flares and sunspots, I found that the value of r can vary quite significantly depending on the specific parameters (sunspot groups, area, morphology) examined. The same might apply to these tissue samples - which means further studies are definitely needed.

Not to put too fine a point on it, but the authors themselves caution that the study isn't a license to engage in unhealthy behavior, e.g. increasing smokes or not using sunblock.

Maybe they definitely know the limits of that correlation coefficient after all!

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